This invention is concerned with the art of supplying fuel to internal combustion engines. It is more particularly concerned with removing drainage of fuel and oil from the crankcase of the engine and mixing it with fuel from the main fuel supply tank enroute to the intake manifold.
In certain internal combustion engines, such as the two-stroke cycle engine, the crankcase serves as a portion of the engine induction system. There the fuel and air mixture from the carburetor passes through a valving arrangement into the crankcase and subsequently through an intake port to the engine cylinder. The outward stroke of the piston creates a suction condition which causes flow of the fuel-air mixture through a pressure responsive valve into the crankcase. The mixture within the crankcase is pressurized by the inward stroke of the piston so that the mixture flows into the cylinder through the intake port whenever it is exposed by the piston. Thus, the crankcase serves as an intermediate portion of the induction system between the valve arrangement and the cylinder.
During the starting of the engine, as well as during its operation, portions of the vapor in the fuel-air mixture are condensed during passage through the crankcase and accumulate therein. Unsuccessful attempts at starting and excessive choking of the carburetor can add to the accumulation of condensed vapor in the crankcase. In the case of the two-stroke cycle engine where the crankcase serves as a portion of the induction system, it is common practice, for lubrication purposes, to include the lubricating oil in the fuel supply since the fuel and air mixture containing the oil contacts the various operating portions of the engine adjacent the crankcase, as well as the cylinder. With lubricating oil included in the fuel, it is evident that the condensate within the crankcase includes both fuel and lubricating oil.
It is undesirable to have an accumulation of liquid fuel and oil within the crankcase since the liquid can enter a cylinder and become trapped there during the outward stroke of such piston. If sufficient quantities of liquid become trapped in this way between the piston and the cylinder head, "hydraulic lock" will result. This hydraulic lock can be highly destructive to the engine parts due to the incompressible nature of the liquid. Additionally, an accumulation of liquid within the crankcase can vary the fuel-air ratio of the mixture being delivered to the cylinder. This phenomenon can cause faulty operation. Among the difficulties that can arise therefrom are spark-plug fouling, and extremely difficult starting.
To eliminate the accumulation of liquid fuel and lubricating oil in the crankcase of two-stroke cycle engines, drain arrangements have been customarily provided in the crankcase. These drains vent the liquid from the crankcase and release it altogether from the engine. The common way of such release is by means of the exhaust system. A common valving arrangement is to provide valves which are responsive to the fluctuating pressure within the crankcase.
It is obvious that venting this liquid directly from the engine is an inefficient practice, because the liquid is composed of fuel and lubricating oil, i.e., the ingredients of the normal fuel mixture, which, if recovered, can be consumed by the engine. It is equally clear that venting the liquid into the exhaust system causes the escape of unpleasant fumes and vapors as the liquid is swept from the engine along with hot exhaust gas. In addition, their escape in sufficient volume can constitute a significant fire and explosion hazard.
In the case of outboard motors for boats, where the two-stroke cycle is the standard type of engine used, the venting of the liquid directly overboard through the exhaust system which passes underwater can cause contamination of the water upon which the boat is operated.
In one of my previous inventions, now U.S. Pat. No. 3,128,748 and entitled "Apparatus and Method for Recovering Engine Drainage," there is shown a system for delivering the fuel and oil drainage from the engine crankcase to the fuel tank of the engine fuel system. This can be done by utilization of gravity only, or by means of a pump. The latter idea is shown in my application Ser. No. 180,593, filed Mar. 19, 1962, now abandoned and entitled "Apparatus and Method for Pumping Engine Drainage."
These systems, although alleviating the above-described difficulties, led to some complications. Since the lubricating oil mixed with the fuel is much less volatile than the fuel, the proportion of oil in drainage recovered from the crankcase significantly exceeds the proportion of oil in the fuel mixture that is normally delivered to the engine. Thus, the ratio of oil to fuel in the drainage is much higher than that of the fuel mixture recommended by fuel manufacturers.
Experience showed that during operation of an engine having the drainage recovery provisions of my above-described inventions, there is a tendency for the drainage to enter the fuel tank and accumulate near its bottom, since the oil-rich mixture is denser than the normal fuel and oil mixture within the fuel tank. Unless recovered drainage is well distributed within the mixture contained within the fuel tank, areas or "pockets" of liquid with excessive oil content will appear. When this excessively oil-rich mixture is drawn from the fuel tank into the carburetor and intake manifold, it causes an undue accumulation of deposits within the cylinders and on the pistons. This phenomenon also results in greatly shortened spark-plug life and an undesirable amount of smoke in the engine exhaust.
These difficulties were alleviated by the invention described in my U.S. Pat. No. 3,528,395 issued on Sept. 15, 1970 and entitled "Apparatus and Method for Mixing Engine Drainage into the Fuel Flow to an Engine." In this patent, there is disclosed a dual-chambered device located entirely outside of the main fuel tank and employing an upper or drainage chamber connected to the crankcase for accumulating drainage and a lower or mixing chamber connected in series with the principal fuel line. Drainage is dropped through an aperture at the bottom of the drainage chamber directly into the fluid in the mixing chamber. It has been found, however, that with this device the possibility exists of heavy concentrations of the drainage fluid being formed in the mixing chamber.